ELECTROCHEMICAL IMPREGNATION OF NICKEL-HYDROXIDE IN POROUS-ELECTRODES

The nickel hydroxide electrode is widely used in several alkaline storage batteries. It is usually manufactured by a chemical impregnation process. A relatively new electrochemical impregnation process is investigated in which the nickel hydroxide is directly precipitated within the porous nickel electrode following the electrochemical reduction of nickel nitrate solution.; An experimental and theoretical study has been conducted to investigate the electrochemical impregnation of nickel hydroxide in porous electrode. The reduction of nitrate was initially conducted at a rotating nickel electrode in acidic 3.0 M nickel nitrate solution at various pH. The rate of nitrate reduction in acidic solution is hydrogen ion diffusion-limited. The impregnation of nickel hydroxide was conducted in a static porous nickel electrode. It is concluded that the loading level and the plaque expansion are the important parameters to be considered. The effects of applied current density, stirring, ratio of solution to plaque volume, and pH have been identified. A novel flow-through electrochemical impregnation is proposed in which the electrolyte is forced through the porous nickel plaque. The thickening of the plaque can be reduced while maintaining high loading capacity. The loading curve under flow conditions is characterized by two plateaus, the first is exclusively associated with the flow-through and the second one is obtained after the electrode is plugged.; A mathematical model is presented which describes the transport of the nitrate, nickel, and hydroxyl ions and the consecutive heterogeneous electrochemical reduction of nitrate and the homogeneous precipitation reaction of nickel hydroxide. The model is applied to the simplified case of flat electrode and to the practical case of impregnation within the porous electrode. The distributions of precipitation rate and distribution of active material within the porous electrode are obtained and reasonably compared with experimental results obtained elsewhere by a tracer technique. A semi-empirical model is also proposed which takes into account the plugging of the pores. A pseudo-steady-state model suitable for electrochemical impregnation under flow-through condition is presented and applied to the design of an electrochemical cell in which the electrode is going through structural changes, as in the case of metal-ion removal and flow batteries.